86 PREPARATION AND MOUNTING 
microscope. The common screw-moss may be found in 
great abundance, and shows this denudation of the spores 
very perfectly. Many of these may be easily dried without 
much injury, but they should also be examined in their 
natural state. 
The student should not omit from his cabinet a leaf of 
the nettle and the allied foreign species, the mystery ot 
which the microscope will make plain. The hairs or stings 
may also be removed, and viewed with a higher power than 
when on the leaf, being so transparent as to require no bal- 
sam or other preservative. 
There are few more interesting objects than the raphides 
or plant-crystals, These are far from being rare, but in 
some plants they are very minute, and consequently require’ 
care in the mounting, as well as a high magnifying power 
to render them visible; in others they are so large that 
about twenty-five of them placed point to point would reach 
one inch. Some of these crystals are long and compara- 
tively very thin, which suggested the name (raphis, a 
needle); others are star-like, with long and slender rays; 
while others again are of a somewhat similar form, each ray 
being solid and short. If the stem of rhubarb, or almost 
any of the hyacinth tribe, be bruised, so that the juice may 
flow upon the slide, in all probability some of these crys- 
tals will be found in the fluid. ‘To obtain them clean, 
they must be freed from all vegetable matter by maceration. 
After this they must be thoroughly washed and mounted 
dry. They are also good polarizing objects, giving bril- 
lant colours; but when used for this purpose they must 
be mounted as described in Chapter IV. A few plants 
which contain them may be mentioned here. The Cac- 
tacez are very prolific; the orchids, geraniums, tulips, and 
the outer coating of the onion, furnish the more unusual 
forms. 
The Fungi are generally looked upon as a very difficult 
class of objects to deal with, but amongst them some of 
the most available may be found. The forms of many are 
